There are applications in which video systems require that a person interact with information presented on a display screen. At times, the interaction is to occur while the person is situated at a distance from the display screen. As will be described more fully below, the interaction may be accomplished by remotely controlling a screen cursor in one of a variety of manners. The interactions may include selecting from a variety of choices presented as a screen menu, or "typing" text using an on-screen keyboard. Examples of remote interactive video systems (RIVS) include interactive television (ITV), TV-style Internet browsers, and conference-room video projectors.
One key component of a RIVS is the "pointing" device for controlling the on-screen cursor. The pointing device fulfills a function analogous to that which mice, trackballs, and graphic tablets perform for computers. However, the environment for RIVS presents difficulties that are typically not encountered in operation of a computer. For example, an operator of a RIVS is typically further away from the controlled device than is the operator of a computer. As another example, the operator of a RIVS is more likely to be in an unstructured immediate environment, e.g., an ITV operator seated across a living room from a television set. In many situations, the environment precludes use of conventional computer pointing devices, such as mice. Moreover, a RIVS is rarely equipped with a keyboard, so that the pointing device may have to accommodate the extra burden of providing a text entry.
There are a number of known pointing devices for a RIVS. Most of the known pointing devices implement some variation of a four-key cursor pad on a hand-held controller. The four-key cursor pad is manipulated to step the screen cursor up, down, left or right among various menu choices. Such interfaces emulate the computer keyboard cursor keys used with old-style textural interfaces. However, these interfaces are typically much slower and less intuitive to use than computer mice and other pointing devices developed for modern graphical software interfaces.
In an effort to improve upon cursor control within the RIVS environment, more advanced computer pointing devices of mice and trackballs have been adapted. In one adaptation, a miniature trackball is mounted atop a controller, with the trackball being operated by the person's thumb. The trackball controller is faster than the use of cursor keys and facilitates diagonal moves. Unfortunately, the trackball may require repeated strokes to accomplish large cursor movements and, in general, thumb control taxes the user's thumb dexterity. For example, it is difficult to trace the cursor in a circle on the display screen.
The use of a mouse for ITV cursor control has been demonstrated. The advantage of the mouse is that it provides excellent and intuitive cursor control. The concern is that there may not be a suitable planar operating surface that is convenient to the operator.
A further refinement in the RIVS pointing art is the use of devices that enable control of a cursor by merely gesturing with a controller. These devices may measure the attitude, i.e. pitch, yaw, and possibly roll, of the controller. A first category of such an approach employs light beams to measure attitude. PCT International Publication Number WO 95/19031 describes a system for determining the pointing orientation of a remote unit relative to a fixed base unit. The fixed base unit includes one or more light sources for emitting a light beam. The emitted light is polarized in at least one predetermined orientation. The movable remote unit includes a photodetector for detecting the polarized emitted light. The attitude of the movable remote unit may be determined by measuring the intensity of received light from various directions.
Another implementation of the emitted-light category of measuring attitude is one in which an infrared (IR) signal is beamed from the area of the video display. The IR signal is defocused and is imaged onto a quad photodiode array in the controller. The relative signal amplitudes from the four photodiodes may be used to determine the relative orientation of the controller to a line drawn from the display. One concern is that the system may undesirably flood the room with intense IR, rendering other nearby IR-coupled appliances (e.g., a VCR controller) inoperative. A second concern is that the limited range of transmission of defocused IR signals may render this system of measuring attitude unreliable when the controller is more than a relatively short distance from the video display.
A second category of devices that measure attitude of the controller is one in which inertial navigation principles are employed. Gyroscopes or encoded gimballed masses establish inertial frames in the controllers, against which attitude changes can be measured. The attitude information may then be transmitted to the video display via a radio-frequency link to a small dipole antenna affixed atop the video display.
The third category is related to the first category. A hand-held object that provides cursor control has a number of light sources mounted on one surface. A single electronic camera is directed to capture images of the light sources mounted on a hand-held object. Locations of the images of the light sources are detected in each camera image, and a computer is used to determine the attitude of the light-emitting hand-held object. Such a device is described in U.S. Pat. No. 5,338,059 to DeMenphon.
A closely related need exists in the field of virtual reality. In games, simulations, and other visualization situations, it is often necessary to encode the attitude of a user's head, or other body part. In many cases, systems for encoding head pitch and yaw may be applied to RIVS controllers, and vice versa. One known virtual reality system encodes pitch and yaw by means of instrumented compasses and gravimeters.
While the known cursor control devices and attitude-determining systems operate adequately for their intended purposes, each is associated with a concern or a problem. Operation may be slow or tedious, or may require use of a specific operating surface. Devices and systems that include IR radiation may adversely affect operation of other devices. Attitude-sensing devices that are based on gravity may have difficulty in distinguishing tilting from transverse acceleration, thereby rendering control erratic. This last problem conceivably could be solved by gyro stabilization, but the cost and power consumption make this solution unattractive. Known systems that utilize light detection require adding a second contrivance at the display, again adding additional cost.
What is needed is a method and a system for reliably tracking attitude of a device. What is further needed is such a method and system that is cost efficient when used in controlling a screen cursor or when used in other remote interactive video applications.